1. Field of the Invention
The present invention relates to a thermal processing apparatus and, more particularly, to a thermal processing apparatus, for example, used for conducting epitaxial growth processing, etching, and the like on wafers.
2. Description of the Relevant Art
Hitherto, a radiation thermometer has been frequently used in a thermal processing apparatus for non-contact measurement of the surface temperature of a wafer or the like without scratching the wafer surface and contaminating the atmosphere within a chamber.
FIG. 7 is a diagrammatic sectional view of a conventional thermal processing apparatus of this type wherein a radiation thermometer is arranged, and in the figure, reference numeral 31a represents a vessel body which forms a chamber. The vessel body 31a is made of a material, such as quartz glass which transmits infrared rays, in the shape of an oval in a sectional view. At both ends of the vessel body 31a, an inlet 31b and an outlet 31c for a gas are formed, respectively. A prescribed gas 32 supplied from the inlet 31b passes through the vessel body 31a to reach a wafer 33 and is discharged from the outlet 31c. In a prescribed position inside the vessel body 31a, a susceptor 31d is arranged, which is rotated by a driving means (not shown). The wafer 33 in the shape of a disk as a workpiece is mounted on the susceptor 31d. An apparatus body 31 comprises the vessel body 31a, inlet 31b, outlet 31c, susceptor 31d, and associated parts.
Above and below outside the vessel body 31a, infrared lamps 34a and 34b as a heating means 34 are placed, respectively. These infrared lamps 34a and 34b are connected through wires 35a and 35b to a power supply means 35, respectively. The power supply means 35 is connected through a signal line 36b to a controlling means 36 which comprises a power supply controlling means 36a. On the other hand, in a prescribed position above the wafer 33 outside the vessel body 31a, a radiation thermometer 37 as a temperature measuring means is arranged, which is connected through a signal line 37a to the controlling means 36.
When a radiation light 33a emitted from the top of the wafer 33 penetrates the vessel body 31a (a transmission part 31e) to enter the radiation thermometer 37, a measured temperature Tm of the top of the wafer 33 is obtained through the radiation thermometer 37 based on the brightness signal of the radiation light 33a, the emissivity of the wafer 33, and the like, and this signal s1 is transmitted through the signal line 37a to the controlling means 36. A required electric energy P is computed based on the deviation of the measured temperature Tm from a preset desired temperature TM by the power supply controlling means 36a in the controlling means 36, and this signal P is transmitted through the signal line 36b to the power supply means 35. Then, on the basis of the signal P, prescribed electric energies P1 and P2 (here, P1+P2=P) are distributed and supplied by the power supply means 35 through the wires 35a and 35b to the infrared lamps 34a and 34b, respectively. A thermal processing apparatus 30 comprises the apparatus body 31, heating means 34, power supply means 35, controlling means 36, radiation thermometer 37, and associated parts.
FIG. 8 is a graph indicating changes in the measured temperatures during the time when, after epitaxial growth processing is conducted on a total of seven wafers 33 one by one with the same heating pattern, using a conventional thermal processing apparatus 30 wherein a susceptor 31d (all in FIG. 7) is adjusted to be in a horizontal position, cleaning is conducted on a vessel body 31a (hereinafter, one process wherein, after thermal processing is successively conducted on a prescribed number of wafers 33 with the same operating conditions, vessel body cleaning is conducted, is referred to as one chance), and these steps are successively repeated. In the figure, X shows a measured temperature Tm of the top of the wafer 33, while ◯ shows a measured temperature Tp of the bottom of the susceptor 31d measured using a thermocouple thermometer (not shown) separately arranged.
As is obvious from FIG. 8, the measured temperature Tm of the top of the wafer 33 measured using a radiation thermometer 37 (FIG. 7) is kept about a prescribed value (about 1125xc2x0 C.) at all times. On the other hand, the measured temperature Tp of the bottom of the susceptor 31d measured using the thermocouple thermometer rises by degrees from about 1125xc2x0 C. to about 1129xc2x0 C. as the number of processed wafers 33 increases from 1 to 7. Then, the vessel body cleaning makes it back to the original temperature of about 1125xc2x0 C. This means that the transmissivity of a radiation light 33a in the vicinity of a transmission part 31e (both in FIG. 7) gradually decreases every time one wafer 33 is processed, so that the temperature of the top of the wafer 33 becomes apparently lower. Therefore, extra power is supplied to a heating means 34 (FIG. 7) to keep the desired temperature (about 1125xc2x0 C.), leading to a substantial rise in the temperature Tp of the bottom of the susceptor 31d. 
FIG. 9 is a graph indicating changes in the measured temperatures during the time when, after epitaxial growth processing is conducted on a total of seven wafers 33 one by one in a state where a prescribed electric energy P is regularly supplied to a heating means 34 as a test pattern, using a conventional thermal processing apparatus 30 wherein a susceptor 31d (all in FIG. 7) is adjusted to be in a horizontal position, cleaning is conducted on a vessel body 31a, and these steps are successively repeated. In the figure, X shows a measured temperature Tm of the top of the wafer 33, while ◯ shows a measured temperature Tp of the bottom of the susceptor 31d measured using a thermocouple thermometer (not shown) separately arranged.
As is obvious from FIG. 9, the measured temperature Tp of the bottom of the susceptor 31d measured using the thermocouple thermometer is kept about 1125xc2x0 C. at all times. On the other hand, the measured temperature Tm of the top of the wafer 33 measured using a radiation thermometer 37 (FIG. 7) falls by degrees from about 1125xc2x0 C. to about 1118xc2x0xc2x0 C. as the number of processed wafers 33 increases from 1 to 7. Then, the cleaning of the vessel body 31a makes it back to the original temperature of about 1125xc2x0 C. This supports that the transmissivity of a radiation light 33a in a transmission part 31e (both in FIG. 7) gradually decreases every time one wafer 33 is processed, so that the measured temperature Tm of the top of the wafer 33 becomes apparently lower.
FIG. 10 is a graph indicating changes in temperature when epitaxial growth processing is conducted on one wafer 33 with a prescribed heating pattern, using a conventional thermal processing apparatus 30 wherein the wafer 33 is mounted in a slightly tilted condition on a susceptor 31d (all in FIG. 7), being rotated. In the figure, (A) shows the desired temperature TM, (B) shows the measured temperature Tm of the top of the wafer 33, and (C) shows the measured temperature Tp of the bottom of the susceptor 31d measured using a thermocouple thermometer (not shown) separately arranged.
As is obvious from FIG. 10, the measured temperature Tm of the top of the wafer 33, the desired temperature TM, and the measured temperature Tp of the bottom of the susceptor 31d are not in agreement with one another, and the measured temperature Tm of the top of the wafer 33 periodically repeats small fluctuations. The periodic fluctuations are in tune with the rotation period of the susceptor 31d. This means that the measured temperature Tm measured using a radiation thermometer 37 is liable to periodically fluctuate because of the mirror surface of the wafer 33 when the wafer 33 is mounted not horizontally but in a slightly tilted condition.
As described above, in the above thermal processing apparatus 30, decomposed components from a gas 32 or the wafer 33 are liable to be deposited on the top of the wafer 33 or the inner wall of the vessel body 31a during the process of epitaxial growth processing or etching. Then, the vessel body 31a and the mirror-like top of the wafer 33 tarnish, so that the transmissivity of the vessel body 31a and the emissivity of the wafer 33 are likely to be lowered. Furthermore, the thickness of the deposit (not shown) and the deposited place tend to vary depending on the temperature of the inner wall of the vessel body 31a and the frequency of use thereof, the kind, flow velocity, and distribution channels of the gas 32, or the timing of removing the deposit (cleaning the vessel body 31a), so that it is difficult to accurately measure the temperature of the top of the wafer 33 at all times during the process of epitaxial growth processing or etching. When the susceptor 31d is rotated, the slight tilt of the wafer 33 makes it difficult to accurately measure the temperature of the top of the wafer 33, and it is difficult to accurately measure the temperature of the bottom of the rotating susceptor 31d using the thermocouple thermometer. As a result, it is difficult to supply an appropriate electric energy P to the heating means 34, so that it becomes difficult to make the temperature Tm of the top of the wafer 33 closer to the desired temperature TM, leading to a possibility that the quality of the wafer 33 after the epitaxial growth processing or etching becomes unstable.
The present invention was accomplished in order to solve the above problems, and it is an object of the present invention to provide a thermal processing apparatus, whereby the temperature of a wafer can be accurately measured at all times, so that epitaxial growth processing and etching can be conducted on the wafer while the wafer is kept at a prescribed temperature, resulting in the improvement in quality of the wafer as a semiconductor substrate.
In the case where an apparatus body 31 shown in FIG. 7 is used, when the rate of flow of a gas 32 running on the top side of a wafer 33 is set to be relatively larger than that running on the bottom side of a susceptor 31d, while a supplied electric energy P1 to upper infrared lamps 34a is set to be relatively larger than that to lower infrared lamps 34b, the deposition of decomposed components onto the inner side surface of a vessel body 31a can be prevented comparatively well.
FIG. 11 is a partial enlarged curve fully showing a 2-cycle portion of the measured temperature Tm of the top of the wafer shown in FIG. 10. As is obvious from FIG. 11, the measured temperatures Tm of the top of the wafer 33 generated with the rotation of a susceptor 31d (both in FIG. 7) almost form a sine wave. Therefore, when a correction for eliminating the sine wave component is conducted, the temperature of the top of the wafer 33 can be accurately measured even if the wafer 33 is not mounted horizontally on the rotating susceptor 31d. 
On the basis of the above knowledge, the present inventors completed the present invention as follows.
In order to achieve the above object, a thermal processing apparatus (1) according to the present invention is characterized by being a thermal processing apparatus comprising a heating means, a power supply means to supply electric power to the heating means, a controlling means to control a supplied electric energy to the heating means, and a first temperature measuring means to measure the temperature of a workpiece through a member which transmits infrared rays, wherein the controlling means comprises a learning-modifying means to learn and modify an output from the first temperature measuring means based on the output from the first temperature measuring means, a supplied electric energy to the heating means and/or an output from a second temperature measuring means separate from the first temperature measuring means.
Using the thermal processing apparatus (1), since the controlling means comprises a learning-modifying means to learn and modify an output from the first temperature measuring means based on the output from the first temperature measuring means, a supplied electric energy to the heating means and/or an output from a second temperature measuring means separate from the first temperature measuring means, the temperature of the workpiece can be accurately measured at all times even if a deposit adheres to the member, or the infrared ray transmission performance of the member deteriorates. Even when the workpiece is a wafer, epitaxial growth processing and etching can be reliably conducted thereon as the temperature thereof is kept at a desired temperature. As a result, the quality of the wafer as a semiconductor substrate can be improved.
A thermal processing apparatus (2) according to the present invention is characterized by being a thermal processing apparatus comprising a heating means, a power supply means to supply electric power to the heating means, a controlling means to control a supplied electric energy to the heating means, and a first temperature measuring means to measure the temperature of a workpiece through a member which transmits infrared rays, wherein the controlling means comprises a rotational component eliminating means to control so as to eliminate a periodically fluctuating signal component which appears in an output from the first temperature measuring means with the rotation of the workpiece.
Using the thermal processing apparatus (2), since the controlling means comprises a rotational component eliminating means to control so as to eliminate a periodically fluctuating signal component which appears in an output from the first temperature measuring means with the rotation of the workpiece, the temperature of the workpiece can be accurately measured at all times even when the workpiece is rotated. As a result, almost the same effect as in the case of the thermal processing apparatus (1) can be obtained.
A thermal processing apparatus (3) according to the present invention is characterized by being a thermal processing apparatus comprising a heating means, a power supply means to supply electric power to the heating means, a controlling means to control a supplied electric energy to the heating means, and a first temperature measuring means to measure the temperature of a workpiece through a member which transmits infrared rays, wherein the controlling means comprises both a learning-modifying means to learn and modify an output from the first temperature measuring means based on the output from the first temperature measuring means, a supplied electric energy to the heating means and/or an output from a second temperature measuring means separate from the first temperature measuring means, and a rotational component eliminating means to control so as to eliminate a periodically fluctuating signal component which appears in an output from the first temperature measuring means with the rotation of the workpiece.
Using the thermal processing apparatus (3), because of a synergistic effect of the effects which each of the thermal processing apparatus (1) and (2) has, a more excellent effect can be obtained.
A thermal processing apparatus (4) according to the present invention is characterized by the heating means, being arranged outside a member which transmits infrared rays, and being constituted so as to heat a workpiece using infrared rays in any of the thermal processing apparatus (1)-(3).
Using the thermal processing apparatus (4), the contamination of the workpiece caused by the heating means can be reliably prevented, so that high quality of the workpiece after thermal processing can be ensured.